Interesting that ref 15 (Forest, Stone & Sokolov, GRL33 L01705) is out
of MIT, home of Dick "what-me-worry?" Lindzen.
They have anticipated James' response, I expect:
"When using unifrom priors on all parameters, these new results are
summarized by the 90% confidence bounds of 2.1 to 8.9 K for climate
sensitivity... We note that the upper bound for the climate
sensitivity is sensitive to our choice fo prior, which was truncated
at 10 K. WHen an expert prior for S is used [Forest et al 2002
(Science 295 113-117)] the 90% confidence intervals are 1.9 to 4.7
K... for S... "
All this amounts to is that the dataset in question is insufficient to
constrain S very well. If you really want to know S, you use
allavailable information, which can be embodied in an expert prior. A
non-truncated prior is mathematically unworkable, and a truncated
prior just amounts to a particularly foolish choice of prior. The high
end you get back out (in this case 8.9 K) is pretty much the same as
the high end you put in (10 K) and tells you nothing.
Note the following in the concluding paragraph
"Despite their uncertainties, the paleoclimate results provide data
not directly included in the present framework... and this supports
using a prior influenced by such results."
This is clear enough to the peer audience, but that group is very
narrow, and it seems likely that Matthews and Caldeira are not in it..
I think this raises important questions about intra-scientific
communication, but I don't think it means we need to worry about a 9 C
sensitivity.
In other words, just because you can't tell by looking at the clouds
whether it is Tuesday does not make the day of the week unknown. It
just means that information is not encoded very clearly in the clouds.
One trouble with science is that stuff gets misused by non-target
audiences. I see no reason to believe that Forest is actually worried
about a nine degree sensitivity on the basis of this paper.
As far as nonstatisticians are concerned, it pretty much looks like
it's 3 C or a smidge under. Can we move on please?
mt
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